I think this use to be true, but with the explosion of the Internet and all of its information(i.e other people's experience), both can be just as easy.
Actually, my 70g is more demanding than my daughter's 7g. I can go months without changing the water in her tank, and he sees no algae growth or bad signs. I fight algae weekly in my tank.
Throw in all the extra equipment in the big tank, and it's hard to say that bigger is easier. Obviously the bigger the volume the more room for error, but with auto-top off and a $100 controller for lights and temperature, small tanks can be a piece of cake if you aren't over stocked. For the record, I'm not advocating no water changes for months. She doesn't have any demanding corals, so that helps me get away with it. I don't understand how she gets literally no algae. It's really not fair.
Mark